1. Field of the Invention
The present invention relates to a liquid ejection inspecting method, liquid ejection inspector and image forming apparatus. More particularly, the present invention relates to a liquid ejection inspecting method and liquid ejection inspector in which inspection of liquid ejection to check failure can be effected efficiently without waste of consumables, and an image forming apparatus for use with the liquid.
2. Description Related to the Prior Art
An ink jet printer is known as an image forming apparatus. A printhead includes an ink reservoir for storing ink. Ejection nozzles are connected with the ink reservoir, and caused by an ink supply unit to eject the ink to print an image on a recording medium. The ink jet printer of the type known so far has problems in that ink is dried and deposited on the inside of the ejection nozzles, or that the surplus ink may be scattered by the recording medium, and come back to and deposit on a surface of the printhead, to cause jamming of ink.
When jamming of ink occurs, there is ejection failure in which an amount of ejected ink decreases, or comes down to zero. Unevenness in the density or colors occurs in a streak shape in a recorded image, to lower the image quality remarkably. Therefore, it is necessary in an ink jet printer to detect the ejection failure at the ejection nozzles, and to eliminate the ejection failure in the case of occurrence.
To check the ejection failure, various methods are known. JP-A 8-332736 and 11-078051 disclose test printing to eject test ink to the recording medium and inspection of the shape and arrangement of droplets of the ink. JP-A 11-192726, EP-A 1059172 (corresponding to JP-A 2001-054954), and JP-A 2001-063083 disclose methods in which droplets of test ink are ejected, a beam of laser or other electromagnetic rays is applied to the droplets, to detect a shielded state of the beam at the droplets.
However, those known techniques have problems. In the first of those methods, a test pattern must be recorded together with a target image without any relation. Also, ink for test printing is required in a wasteful manner. A space in the recording medium for receiving droplets of the ink is required for the test printing. In the second of those methods, the same problem occurs in ink for test printing is required in a wasteful manner. Specifically, density in image recording has been higher in recent techniques for printing. The number of the ejection nozzles as arranged in the printhead has been high. This causes a shortcoming in requirement of much time for the detecting the ejection failure. If the ejection failure is checked in the course of the printing, productivity or efficiency in the printing becomes lower.